Upload
doankhanh
View
217
Download
0
Embed Size (px)
Citation preview
Airflow Sciences Corporation ®
1
Aerodynamic Drag Reduction of Open-Top Coal Cars in Unit Train Operation and Impact on Train Fuel
Consumption and Economics
James Paul, P.E., Senior EngineerAirflow Sciences Corporation, Western Region OfficeCarmel, California USA
Coal Car Aerodynamics
National Coal Transportation AssociationSpring General Conference
26 – 29 April 2015Litchfield Park, Arizona
Airflow Sciences Corporation ®
2
Aero Transportation Products, Inc.Independence, Missouri
Airflow Sciences CorporationLivonia, Michigan
Project Participants
30% scale baseline hopper car models in Lockheed Georgia Company wind tunnel at 5⁰ yaw.
®
Airflow Sciences Corporation ®
3
The current study involved two primary tasks:
1) Identify and test candidate retrofit coal car aerodynamic drag reducing devices and rank the devices by
•) Effectiveness
•) Impact on train fuel usage
•) Return on investment
2) Build prototype drag reducing devices and test them at full scale to verify durability and fuel savings
Project Overview
16% Scale Gondola Car Models in National Research Council of Canada 9 M Wind Tunnel (8 car train)
Airflow Sciences Corporation ®
4
Presentation Outline
Coal Car Aerodynamics
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Conclusions and Recommendations
30% Scale Model High-Side Gondola Car, No Internal Bracing, Lockheed Georgia Company Low Speed Wind Tunnel
Airflow Sciences Corporation ®
5
Definition of North American Coal Car Fleet
Lessors78,666 Cars
(29%)
Total Number of Coal Cars in
North American Fleet:
267,000
Summary of North American Coal Car Fleet Population and Ownership
Railroads107,065 Cars
(40%)
Utility Companies81,269 Cars
(31%)
Lessors78,666 Cars
(29%)
Project Overview
Airflow Sciences Corporation ®
6
Coal Car Aerodynamics
Classifications of Aerodynamic Modifications for Open-Top Gondola and Hopper Cars
• Covers • Inter-Car Spacing and Gap Fillers • Internal Baffles • Car Side Geometry• Underbody • End Treatments
Typical Hopper Car Typical Gondola Car
Image: FreightCar America Image: FreightCar America
Airflow Sciences Corporation ®
7
Coal Car Aerodynamics: Ranking of Coal Aerodynamic Devices
Drag Area = Cd A (ft2)
from: Cd = D /A q
where: D = Drag Force (lbs)Cd = Drag Coefficient (non-dimensional)A = Cross Sectional Area of Coal Car (ft2)q = Dynamic Pressure of Air = ½ V2
= Density of Air (slugs/ft3)V = Air Velocity (ft/sec)
thus: D = [Drag Area] q
Terminology: It is convenient to group the drag coefficient and cross sectional area together and refer to them collectively as the drag area. This eliminates any confusion regarding the selected value for the cross sectional area.
Airflow Sciences Corporation ®
8
Coal Car Aerodynamics: Ranking of Coal Aerodynamic Devices
Aerodynamic Drag of Train = (½ V2) Cd AWhere ρ = air density, V = Train Speed, Cd = Drag Coefficient, and A = Frontal
Area
Aerodynamic drag at 60 miles/hour is 2.25 times greater than aerodynamic drag at 40 miles/hour.
Aerodynamic Drag increases with the square of velocity
Power increases with the cube of velocity
This graph is based on a unit train without aerodynamic modifications
Airflow Sciences Corporation ®
9
Coal Car Aerodynamics: Ranking of Coal Aerodynamic Devices
Power Required to Overcome Aerodynamic Drag = (½ V2) Cd A VWhere V = Train Speed
Power required at 60 miles/hour is 3.4 times greater than power required at 40 miles/hour.
Aerodynamic Drag increases with the square of velocity
Power increases with the cube of velocity
This graph is based on a unit train without aerodynamic modifications
Airflow Sciences Corporation ®
10
Coal Car Aerodynamics: Covers
Influence of Covers on Coal Car Drag Coefficient
Airflow Sciences Corporation ®
11
Coal Car Aerodynamics: Internal Baffles
Observed Flow Behavior in Vicinity of Open-Top Rail Cars
Calculated Flows and Pressures Along Car Centerline
Surface Pressure (inches of water)
Flow Separation Occurs at Sharp-Edged Corners
Airflow Sciences Corporation ®
12
Coal Car Aerodynamics: Internal Baffles
Car Centerline Velocities and Pressures (with and without baffles); from 3-D CFD Model.
Train DirectionStatic Pressure
Without Baffles
With Baffles
Baffles prevent high velocity air from entering car interior.
Airflow Sciences Corporation ®
13
Coal Car Aerodynamics: End Treatments
Gondola Car End Treatments
Wind Tunnel Test of Airfoils
End Treatments on Pullman Standard Pegasus Car
End Treatments on 30% Scale Wind Tunnel Model
• Adding fairings to the tops of the vertical end walls has been shown to reduce aerodynamic drag of empty cars from 16% to 20%.
• The level of drag reduction depends upon the sophistication of the add-on designs.
Airflow Sciences Corporation ®
14
Coal Car Aerodynamics: Ranking of Coal Aerodynamic Devices
• To rank the effectiveness of the drag reducing devices, the concept of Wind-Averaged Drag (WAD) Coefficient is introduced.
• The wind-averaged drag coefficient represents a typical yaw angle based on average wind speeds and train routes in North America. It is defined in SAE Publication J1252.
• The average North American train speed is 43 miles/hour (70 km/hr). The average North American wind speed is 6.8 miles/hour (11 km/hr).
• This produces a wind averaged yaw angle of between 5º and 6º from which the wind-averaged drag value can be determined.
Wind-Average Yaw Angle:
Wind Averaged Yaw Angle θ = 5.5
Airflow Sciences Corporation ®
15
Coal Car Aerodynamics: Ranking of Coal Aerodynamic Devices
Effectiveness of Aerodynamic Drag Modifications on Coal Car Wind-Averaged Drag
Airflow Sciences Corporation ®
16
Presentation Outline
Coal Car Aerodynamics
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Conclusions and Recommendations
BNSF Unit Coal Train Leaving Powder River Basin, Wyoming
Airflow Sciences Corporation ®
17
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Energy and Fuel Usage Calculations(Spread-Sheet Method)
To determine the energy required for a given train journey, we divide the track into segments and determine the forces acting along each segment:
If F(x) = total resistance force acting on train, the energy required to overcome this force is given by the following formula:
Airflow Sciences Corporation ®
18
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Calculations Based on Fuel Usage Spread-Sheet Method:
Components of Resistive Force Acting on Train:• Gravity (Elevation Changes)
• Rolling Resistance (Including Journal Bearings)
• Acceleration (F = ma) for starting and speed changes• Flange Resistance (Curves)
• Aerodynamic Drag High Speed Unit Train a. From Mine to Power Plant
Energy Expended % ofResistance Force (ft-lbs) (BTU) (MJ) TotalElevation Changes 0.0000E+00 0.0000E+00 0 0.00Rolling Resistance 2.0094E+11 2.5841E+08 272,437 53.16Acceleration: Starting Resistance 2.9719E+09 3.8219E+06 4,029 0.79
Speed Changes 3.2860E+10 4.2258E+07 44,552 8.69Flange Resistance (Curves) 5.0743E+09 6.5255E+06 6,880 1.34Aerodynamic Drag 1.3613E+11 1.7506E+08 184,564 36.02
Totals: 3.7798E+11 4.8608E+08 512,461 b. From Power Plant to Mine
Energy Expended % ofResistance Force (ft-lbs) (BTU) (MJ) TotalElevation Changes 1.5036E+10 1.9336E+07 20,385 5.17Rolling Resistance 5.4897E+10 7.0597E+07 74,429 18.87Acceleration: Starting Resistance 4.0596E+08 5.2207E+05 550 0.14
Speed Changes 8.9773E+09 1.1545E+07 12,171 3.09Flange Resistance (Curves) 1.3863E+09 1.7828E+06 1,880 0.48Aerodynamic Drag 2.1029E+11 2.7044E+08 285,118 72.27
Totals: 2.9100E+11 3.7422E+08 394,534
Typical Energy Model Calculation Summary
Airflow Sciences Corporation ®
19
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Calculations Based on Fuel Usage Spread-Sheet Method:
Train Energy and Economics Model Input Parameters
Example Energy and Economics Model Input
Airflow Sciences Corporation ®
20
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Calculations Based on Fuel Usage Spread-Sheet Method:
For these examples the energy required to transport the empty coal cars back to the mine requires between 60% and 80% of the energy required to transport the loaded cars from the mine to the power plant.
Airflow Sciences Corporation ®
21
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Calculations Based on Energy and Fuel Usage Model:
Example Output File: Energy Section of Train Energy and Economics Model (Baseline Gondola)
Airflow Sciences Corporation ®
22
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Fuel Usage Calculations:
Comparison of Fuel Measurements to Results of Energy Simulation
Airflow Sciences Corporation ®
23
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Calculations Based on Fuel Usage Spread-Sheet Method:Example Output: Economics Section of Train Energy and Economics Model
Assumptions: Diesel Fuel Cost: $3.02/gallon Freight Through Rate: $18.00/net delivered ton mile Number of Trips per Year per Car: 35
Fuel Savings Per Round Trip: mine-to-power plant and power plant-to-mine
Airflow Sciences Corporation ®
24
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Calculation of ROI for Retrofit Aerodynamic Devices:
To determine the return on investment (ROI) associated with the candidate retrofit aerodynamic devices, the following procedure was followed:
Calculate the fuel savings associated with each device using the spread-sheet-based calculation procedure. Multiply by the fuel cost to obtain the savings in dollars per car per year.
Subtract the lost revenue (due to displaced payload) associated with the weights of the add-on aerodynamic devices to obtain the Net Cost Reduction (dollars per car per year).
Divide the cost of the retrofit aerodynamic device (dollars per car) by the Net Cost Reduction to obtain the ROI (years).
Airflow Sciences Corporation ®
25
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Lost Revenue due to Weight of Retrofit Aerodynamic Devices:
Assumptions: Freight Through Rate: $18.00/net delivered ton mile Number of Trips per Year per Car: 35
Airflow Sciences Corporation ®
26
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Calculation of ROI for Retrofit Aerodynamic Devices:
Assumptions: Diesel Fuel Cost: $3.02/gallon Freight Through Rate: $18.00/net delivered ton mile Number of Trips per Year per Car: 35
Airflow Sciences Corporation ®
Flow Separation Point
27
AirFoil Design
Surface Velocities
Direction of Air Flow
Aerodynamic Design of AirFoils
Constant Velocity Region
Pressure Recovery Region
Inside Rear Wall of Car
Location of Peak Velocity
Exterior Airfoil
Constant Velocity Region: In this region, velocities along the surface are higher than freestream, creating a low pressure area that produces a force acting in the direction of travel.
Pressure Recovery Area: In this region, the air velocities are decreased in a controlled manner to prevent flow separation and resulting energy loss.
Cross Section of AirFoil
The AirFoil geometry was developed using computational fluid dynamics modeling and boundary layer separation theory.
Airflow Sciences Corporation ®
28
Power Reduction
Surface Velocities
Power Reduction due to Addition of AirFoils
Impact of AirFoils on Power Required for Unit Train of EMPTY Cars Operating on Tangent, Level Track (100 Empty Coal Cars + 4 Locomotives)
Coal Car Configuration
Train Speed(miles/hour)
Power Required(HP) Power Reduction Due
to Addition of AirFoilsWithout AirFoils 40 4,855
60 14,076
With AirFoils 40 4,244 10% to 13%
60 12,014 14% to 15%
Airflow Sciences Corporation ®
29
Impact of Fuel Use
Surface Velocities
• The projected fuel savings for a round trip unit train from coal mine to power plant (loaded cars on outbound leg and empty cars on return leg), varied from 5.4% to 8.1%, depending upon the coal car type, train speed histogram, and coal pile geometry.
• For other car, train speed, and coal pile combinations, most notably, flat-floor gondola cars, the payback period resulting from addition of AirFoils can be as short as 1.4 years.
Impact of AirFoils on Fuel Use: Unit Train Round Trip
Airflow Sciences Corporation ®
30
AirFoil Durability
Surface VelocitiesAirFoil Durability Testing:
In-Service Evaluations; Photos of Car Loading Operation
Test cars have been in service for over 3 years.
AirFoils do not limit load capacity of cars
AirFoils do not impede car loading or unloading operations
Airflow Sciences Corporation ®
31
Presentation Outline
Coal Car Aerodynamics
Impact of Candidate Aerodynamic Devices on Train Fuel Economy
Conclusions and Recommendations
Surface Velocities
AirFoils Exterior (left) and Interior (above) Views
Airflow Sciences Corporation ®
32
Conclusions and Recommendations
Coal Car Aerodynamics: Conclusions
• Aerodynamic drag represents over 70% of the tractive effort required to move an empty unit coal train and over 36% of the tractive effort required to move a loaded unit coal train.
• The energy required to transport the empty coal cars back to the mine requires between 60% and 80% of the energy required to transport the loaded cars from the mine to the power plant.
• Retrofit aerodynamic devices, including covers, baffles, smooth sides, AirFoils, and side skirts, are effective at reducing aerodynamic drag of both loaded and empty coal cars. Aerodynamic drag reductions can be as high as 44% - 50% for covers, and 17% - 20% for AirFoils.
Airflow Sciences Corporation ®
33
Conclusions and Recommendations
Coal Car Aerodynamics: Conclusions
Fuel savings per round trip (mine-to-power plant and power plant-to-mine) resulting from addition of aerodynamic devices ranges from 2% to 20%, depending upon car type and train speed history. Flat covers and combinations of modifications produce the greatest drag reductions.
Aerodynamic retrofit devices add weight to the car and impact the load capacity. Some devices, for example dome-style covers, can increase car weight by over 1.5 tons.
The projected fuel savings for a round trip unit train equipped with AirFoils varies from 5.4% to 8.1%, depending upon the coal car type, train speed histogram, and coal pile geometry.
Airflow Sciences Corporation ®
34
Conclusions and Recommendations
Coal Car Aerodynamics: Conclusions
An economic evaluation indicates AirFoils offer the best return on investment for the aerodynamic devices evaluated. Payback periods range from a high of 4.8 years for low-speed routes to 1.4 years for higher speed routes.
Reducing train fuel use impacts greenhouse gas emissions. Reducing GHG emissions may provide opportunities for carbon credits.
Based on industry publications, the U.S. transportation of coal requires on the order of 1.5 billion gallons of diesel fuel each year. Thus, a 5% fuel savings would be 75 million gallons, or 2% of all Class I railroad fuel consumption.
Airflow Sciences Corporation ®
35
Contact Information
James C. Paul, P.E. Steve Early
Senior Engineer V.P. Engineering
Airflow Sciences Corporation Aero Transportation Products
Western Region Office Independence, Missouri
Tel.: 831-624-8700 Tel.: 800-821-2376
E-Mail: [email protected] E-Mail: [email protected]